Case Study – Enabling Firmwareless Motorized Medical Arm Position Control

The Problem

Interventional Systems is a medical equipment manufacturer resonsible for Micromate™ – a robotics platform for micro-invasive interventions. They were designing an articulated arm for interventional radiologists and oncologists that could hold surgical equipment in a fixed position. This would remove the need for manual holding, reduce physical strain on the medical experts performing procedures, increase patient safety, and reduce intervention time.

Challenges

With patient safety as a priority, there were numerous limitations in the way the project could be realized. The device could not be powered directly by an outlet, as to not create an electrical hazard and/or harm to patients. No physical connector (such as a USB port) could be used, in order to prevent the device from getting damaged due to contact with liquids or disinfectants used in the operating room.

Since every part of a medical device needs to undergo a rigorous certification process, it was extremely complicated to have any kind of software to operate the motor. Finally, due to the articulated arm’s size, there were significant constraints on the dimensions of the battery, motor, and electronics.

The Solution

Button-operated position locking

Once the robotic arm is placed in the desired position, it needs to be safely locked into place. This requires manually tightening a wing bolt on the arm’s joint. To avoid this, the client wanted to enable locking and unlocking the arm by simply pressing a button.

For maximum patient safety and to avoid accidentally pushing a button, the design requires two buttons on the sides of the device to be simultaneously pushed to lock or unlock the arm.

Following a minimalist design, there are two sets of buttons on the sides along with a multicolor LED light that indicates the state of the device (charging, locked, unlocked, low battery, etc.).

A firmwareless solution

The motor turning the bolt needs to provide a certain amount of torque to lock a joint and is powered by the battery. Typically, this kind of system would be controlled by a microprocessor running custom-written software. Due to the solution being a part of a medical device, if the hardware were software-controlled, the software itself would have to pass the certification process.

To avoid this time-consuming, complex, and costly option, NOVELIC took on an unconventional approach by designing a discrete electronics circuit able to control the motor without any software.

Wireless charging

Plugging devices directly into a power outlet should be avoided in the operating room. With the additional requirement of the device having no connectors, our team set out to design a wireless charging cradle.

The cradle communicates with the device using the Qi protocol, an interface standard for wireless power transfer using inductive charging. The cradle itself can be charged anywhere outside the operating room through a power adapter. A fully charged battery allows for at least 30 locking and unlocking cycles between recharges.

Size limitations

The number of required lock/unlock cycles between charges is dictated by the battery capacity, which in turn dictated its size. To fit the battery, motor, and the electronics inside the arm, our team used a Rigid-Flex PCB with bending abilities as a method of stacking PCBs, which helped overcome the space constraint.

Risk analysis and medical certification

NOVELIC performed a thorough risk analysis of all possible scenarios that could lead to patient’s harm (device malfunctioning, overheating, not charging properly, etc.). During the precertification process, our team ensured that the device does not transmit or receive electromagnetic signals above the defined limits. The lithium battery was certified at a battery manufacturer to obtain the UN/DOT 38.3 certification that allows air transportation. Finally, the whole device was certified in the United Kingdom to ensure compliance with IEC 60601-1:2005+AMD1:2012, including relevant national deviations.

Highlights

• Easy-to-use arm positioning
• Firmwareless control
• Wireless charging
• Small dimensions​

Simple button-operated locking/unlocking

Maximum Patient Safety

Fully-certified Medical Device